In the arts of cooking and making of flavors it is well known that the human senses of smell and taste are very closely related. In cooking when a chef wants to check a certain dish he usually smells it before tasting it. Similarly a wine conoisseur smells the "bouquet" of a wine before sampling it.
In the art of making flavors, most staple ingredients are volatile. A flavorist who is trying to either create a new flavor or improve an existing one also used his sense of smell extensively. When his combination of ingredients has an acceptable aroma he knows that he is close to his target. However, in order to reach this point, the flavorist must actually mix the ingredients together before he can smell them. Some flavors require hundreds of ingredients. Furthermore, the amount of certain ingredients used in any given flavor is also critical for obvious reasons. Thus the process of flavor making is very long and painstaking.
One method that has been used to obviate the need for mixing the ingredients before smelling them is to dip a so-called smelling blotter in a bottle containing each ingredient and then placing them in close proximity to each other. The vapors from each ingredient mingle together. Obviously, this method may be used with only literally a handfull of ingredients. Furthermore, the method does not reveal any quantitative information.
The above considerations are vary applicable in the art of making frangrances.